This invention relates to a mechanical assembly for mounting a Liquid Crystal Display (LCD), light guide and electronic circuitry on an internal frame. This assembly provides a single package of low thickness and low weight, while retaining high strength, stiffness and support.
FIG. 1 shows a cross section view of a conventional assembly of a LCD, light guide and circuitry. A LCD 10 commonly has two sheets of glass separated by a sealed-in, liquid crystal material. The application of electrical voltages to this material changes its optical characteristics. By providing a large number of electrically conductive traces on the glass to control individual segments of this material, a display panel can be formed for the display of text and graphics.
While a LCD 10 can rely solely on ambient light falling upon it to be reflected to the viewer, additional viewing flexibility can be provided by using a "backlight" usually situated behind the LCD 10 and directing light through the LCD 10 to the viewer. A common form of backlight shown in FIG. 1 has a Cold Cathode Fluorescent (CCF) light bulb 12 mounted to one side of the LCD 10, whose light is brought underneath and directed upward through the LCD 10 by a plastic light guide 14 that conducts the light sideways and evenly diffuses the light upwards. Light guide 14 can be made of acrylic, polycarbonate or polystyrene with appropriate grooves, scoring, or dispersed material to diffuse light upward into the LCD 10.
It should be noted that a LCD 10 and light guide 14 cannot be directly mounted to each other, since the LCD glass and light guide acrylic have widely different coefficients of expansion with variation in temperature. A directly adhered LCD 10 and light guide 14 would buckle or flex with temperature changes, or would result in damage to the softer light guide material as the LCD glass resisted expansion. Conventional assemblies, such as FIG. 1, use a "wrap-around" metal frame 16 that encloses a LCD 10 against a light guide 14, separated by spacers 15. This conventional assembly allows the individual expansion and contraction of the LCD glass and plastic light guide. These conventional assemblies are quite thick, and heavy as the metal frame 16 adds a layer of metal both above and below, and has metal frame 16 surrounding the entire circumference of the assembly. It is desired to reduce the thickness and weight of these assemblies since they are frequently used in portable equipment.
There is electronic circuitry 18 associated with driving and controlling the LCD 10, and it is desirable to position this circuitry close to the LCD 10 where the large number of electrically conductive traces from LCD 10 are easily accessible. In conventional assemblies as shown in FIG. 1, this circuitry 18 is mounted on a circuitry board 19 below the light guide 14. This requires a large number of interconnections around the edge of the light guide 14 up to the LCD 10 by means of a flexible interconnect, multiconductor flat cable, or "flex-circuit" not shown in FIG. 1. This additional interconnect adds to the complexity, thickness, and cost of the assembly. Alternatively, the circuitry 18 and circuitry board 19 can be mounted at the edge of the LCD 10. This edge position requires that the circuitry 18 and circuitry board 19 be contained within the "wrap-around" metal frame 16, which further increases its size and weight.